During the manufacture of various types of monolithic integrated circuits (ICs) such as high density DRAMs having several thousand transistors fabricated in a single chip of silicon, there are many stages in the multi-level layer wafer processing sequence where it is desirable to provide highly conformal coatings of a selected dielectric insulating material such as silicon dioxide, SiO.sub.2, or silicon nitride, Si.sub.3 N.sub.4. That is, it is desirable to deposit these insulating coatings so that they precisely replicate the geometry of the layers upon which they are formed. This feature ensures that electrical shorts through these very thin dielectric layers are prevented and it further ensures that the packing density and general reliability of the integrated circuit being fabricated are maximized.
Over the years, there have been many different types of thermal oxidation processes, vapor deposition processes and plasma deposition processes used to form oxides, nitrides, carbides, and other dielectric coatings in the manufacture of integrated circuits. Of these processes, there are two types in particular which have been used in recent years in the manufacture of high density DRAMs. The first of these processes is a low pressure chemical vapor deposition (LPCVD) process which may use, for example, tetraethylorthosilicate (TEOS) or diethylsilane (DES) as the silicon-containing reactive compound to form either oxide or nitride coatings on selected substrates. However, there are many attendant disadvantages associated with using low pressure chemical vapor deposition systems, and among these include the fact that these LPCVD systems have to be heated up to temperatures in the range of 450.degree. to 500.degree. C. in order to suitably generate the LPCVD chemical reaction necessary to dissociate the silicon or nitrogen containing compound and deposit the silicon dioxide or silicon nitride layer on a selected substrate.
In addition, the liquid delivery systems for the LPCVD apparatus are difficult to operate and maintain in order to produce reactant gases in the LPCVD deposition chamber, and the dielectric layer deposition rates for these LPCVD systems are difficult to control. Furthermore, these LPCVD systems are difficult to clean, and the device reliability of the semiconductor devices thus produced has not always been acceptable. For example, frequently hillocks and precipitates are produced in aluminum conductive layers over which the silicon dioxide or silicon nitride protective layers are formed.
More recently, plasma enhanced chemical vapor deposition (PECVD) systems have come to replace some of the older LPCVD systems, and generally speaking, PECVD systems have come to be more of a favored choice over LPCVD systems, even though LPCVD systems are still widely used for a variety of materials deposition processes. For approximately the past five years, silane, SiH.sub.4, has been used as the silicon-containing reactive gas in these PECVD systems. However, the problem and disadvantage of using silane as a reactive gas in these PECVD systems is that it is impossible to achieve a conformality of greater than about sixty percent (60%) for the inorganic insulating layers thus formed.
To improve this conformality in the inorganic dielectric layers produced by these PECVD systems, tetraethylorthosilicate (TEOS) has been tried as a possible candidate and suitable reactant gas in PECVD systems for forming silicon-containing dielectric layers on selected substrates. However, there are several distinct disadvantages of using TEOS as the silicon containing compound in PECVD systems. For example, TEOS has a very low vapor pressure and thus must be heated up to a source temperature of greater than 50.degree. C. to produce vapors from a TEOS source and suitable for transporting these vapors from a TEOS source and into a PECVD reaction chamber. This requirement in turn means that special mass flow controllers must be used in these TEOS systems. Additionally, the TEOS gas delivery lines as well as the mass flow controllers must be maintained at a predetermined minimum elevated temperature in order to prevent condensation in the gas flow lines and its associated damage to the chemical processing equipment which can produce significant maintenance problems. Furthermore, the use of TEOS in PECVD systems has been found to produce undesirable variations in dielectric layer deposition rates on selected substrates.